While not a community itself, Terence Tao's blog (https://terrytao.wordpress.com/) is a good source of high quality, clearly explained maths. As you may know, he has a very broad range of interests, and there might be something for you to pick up and get involved in. He has also been involved in several collaborative math communities, which he writes about at length in his blog. I recall Polymath project and recently some project involving Lean Theorem Prover that even showed up on the first page of the HN.
+1!! This may sound weird, but I can use this as a mood booster when life gets tough. Side note: I might be biased because I also find it useful to think about the vastness space to trick my brain falling asleep (I watch a lot of video astronomy videos).
The point Julia makes about `grep` resonate with me alot! I have the same (call it problem if you want) issue with `ps`. There is only one variation of ps I know of (`ps aux`) and if I want to change that I have to either look for the options in the man page or google it.